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Aristotle was, perhaps, the greatest original thinker who ever lived.  Historian H J A Sire has put the issue well: “All other thinkers have begun with a theory and sought to fit reality into it: Aristotle is the only philosopher to have begun with reality and devised a system by which to understand it.”[1]   There is no thinker in the ages that have passed since the fourth century BC who is not in his debt.


There are many misunderstandings among modern scholars over what Aristotle taught.  This is due to a variety of factors.  First, those who read him do so according to their own world view or philosophy which is formed, inevitably of a mix of materialism and subjectivism.  It may include some grasp of metaphysical principle but this is submerged in these powerful forces.  A second influence arises from peer group pressure, an effect of the subjectivist mentality.  If a majority of scholars holds a position as to what Aristotle taught, it is a brave man who would depart from it.  Third is the difficulty over Aristotle’s science.   While his philosophy was profound, his science was tied to the limitations of his age.  It is easy for those without a thorough grounding in metaphysical thought and the discipline of distinction, to see his philosophy through the lens of his science so that, some aspect of his science being found defective, they assume a condign defect in his philosophy.


The following is a summary of important issues where commentators go awry. 


Eternity of Time and Motion, and Efficient Causality

Aristotle was the first philosopher to elaborate the doctrine of causality, showing that of every thing that exists there are four causes—formal, material, efficient and final (Physics Bk. II, ch.vii, 198a 14)—and he insisted that this doctrine applied universally.  Logically, then, he must be taken to assert that it extends to the whole of reality.


He believed that motion and time were eternal (cf. In XII Metaphys. L.5, 2496), though he failed to prove that they were, as St Thomas Aquinas points out (In VIII Physic. L.2, 983).  But it does not follow that he must be taken to have denied that God was the efficient cause of the universe.  That view is grounded in the confusion, driven by the all-pervasive influence of materialism on even the best of our modern thinkers, of the ontological order with the chronological.


St Thomas addresses the issue, quoting from St Augustine:

“Some… philosophers said that the world was eternal, although made by God.  For they hold that the world has a beginning, not of time, but of creation, so that in a certain hardly intelligible way it was always made.  And they try to explain their meaning thus: [I]f the foot were always in the dust from all eternity, there would always be a footprint which without doubt was caused by him who trod on it, so also the world always was, because its Maker always existed.” (De Civ. Dei x. 31)  To understand this we must consider that the efficient cause, which acts by motion, of necessity precedes its effect in time; because the effect is only in the end of the action, and every agent must be the principle of action.  But if the action is instantaneous and not successive, it is not necessary for the maker to be prior to the thing made in duration as appears in… illumination.  Hence they say that it does not follow necessarily if God is the active cause of the world that He should be prior to the world in duration; because creation, by which He produced the world, is not a successive change…”  (Summa Theologiae I, q. 46, a. 2 ad 1)

Hence, that the universe is eternal does not exclude God as its efficient cause.  Now let’s look at what Aristotle actually said.


God the First Efficient cause and the First Being

Aristotle shows (Metaphysics Bk. II 994a 11 to 994b 31) that it is impossible to proceed to infinity in any of the four categories of causes.  He proves the existence of a first efficient cause and of a first material cause in the following text.

“[I]ntermediate things in a series limited by some first and last thing must have as their cause the first member of the series…  Indeed… all parts are intermediate to the same degree right down to the present one.  Therefore, if there is nothing first in the whole series nothing in the series is a cause.”

“[T]here are two ways in which one thing comes from another… either in the way a man comes from a boy… or in the way in which air comes from water.  We say… that a man comes from a boy in the sense that what has come into being comes from what is coming into being, or in the sense that what has been completed comes from what is being completed.  For generation is always midway between being and non-being, and thus whatever is coming into being is midway between what is and what is not… But water comes from air in the sense that it comes into being when the latter ceases to be.

“This is why changes of the former kind are not reversible, and thus a boy does not come from a man.  The reason is that the thing which comes into being does not come from generation but exists after generation… On the other hand, changes of the latter sort are reversible.

“Now in neither way is it possible to proceed to infinity; for existing intermediaries must have some end and one thing may be changed into the other because the corruption of one is the generation of the other.

“At the same time it is impossible that an eternal first cause should be corrupted; for since generation is not infinite in an upward direction, then a first principle by whose corruption something else is produced could not be eternal.”   


St Thomas confirms the proof in his commentary:

“In regard to the first it must be noted that a patient is subjected to an agent.  Therefore to proceed from agent to agent is to proceed in an upward direction, whereas to pass from patient to patient is to proceed in a downward direction.  Now just as action is attributed to the cause of motion, so is undergoing action attributed to matter.  Therefore among the causes of motion the process is in an upward direction, whereas among the material causes the process is in a downward direction [and in neither is it possible to proceed to infinity].”  (In II Metaphys. L.3, 305)


In the Physics Bk. VIII Aristotle shows that the production of the whole of being by the first cause of being is not a motion—

“The necessary presupposition of motion of any kind… is that things capable of motion of that kind should already be in existence.”  (251a 8 et seq.)

Before some being is moved to move it must first be caused to exist.  But since agere sequitur esse, the unmoved mover must be a being that depends on no other for its existence, must exist necessarily.  This is manifested elsewhere in Aristotle’s teaching.  In Metaphysics Bk. XII, 1071b 22 et seq. he proves that God is pure act.  Since something acts only forasmuch as it is in act, and nothing can act absolutely unless it be absolutely, it follows that God is the self-subsistent being.  Therefore the first unmoved mover is the being that exists necessarily, the first uncaused cause.


God the source of matter

In the Metaphysics Bk. II (993b 19-30) Aristotle proves that that which is most true and most being is the cause of the being of all existing things.  He goes on:

“Further, it is evident that there is a [first] principle, and that the causes of existing things are not infinite either in series or in species.  For it is impossible that one thing should come from something else as from matter in an infinite regress as, for example, flesh from earth, earth from air, air from fire, and so on to infinity…”


St Thomas agrees in his commentary on Book VIII of the Physics where he rejects the view that Aristotle did not see God as the source of the existence of matter:

“Hence it follows that the very being in potency which primary matter has is derived from the first principle of being, which is [that which is] most being.  Therefore, it is not necessary to presuppose something for its action which has not been produced by it.  And since every motion requires a subject… it follows that the universal production of being by God is neither motion nor mutation but a certain simple emanation… Therefore, if we were to think that the production of things by God is from eternity, as Aristotle and many Platonists held, it is not necessary—in fact it is impossible—that some non-produced subject be understood for this universal production.”  (In VIII Phys. L.2, 974)


The Perfections of God

In Metaphysics Bk. XII, 1071b 22 et seq., Aristotle details the perfections of God, the first substance—

  • as act unmixed with potency;
  • as living with a life wholly absorbed in intellectual activity;
  • as eternal;
  • as simple (without parts), and therefore immaterial.

At 1072a 26-1072b 14 he asserts the first substance to be immutable and the cause of the eternal motion of the heavens.  He goes on to make the most profound statement made by any man ignorant of God’s revelation: “God is understand, the understand of an understand”.  (1074b 15-1075a 10)[2]


At 1072b 14-1073a 13 he confirms that the first mover is a person:

“Life… also belongs to him, for intellectual activity is life and God is that activity; and the essential activity of God is the life which is best and eternal.  And we say that God is an animal, eternal and most excellent.  Hence life and continuous and eternal duration belong to God; for this is what God is.”

St Thomas comments:

“He says that God is life itself, and he proves this as follows.  ‘Intellectual activity’, i.e., understanding, is a kind of life; and it is the most perfect kind of life that there is.  For… act is more perfect than potency; and therefore an intellect which is actually understanding leads a more perfect life than one which is only potentially understanding, just as being awake is more perfect than being asleep.  But the first being, God, is act itself; for His intellect is His intellectual activity; otherwise He would be related to His intellectual activity as potency to act.  Moreover, it has been shown [Bk. XII, Ch. 7] that His substance is actuality.  Thus, it follows that the very substance of God is life, and that His actuality is His life, and that it is the life which is best and eternal and subsists in itself.  This is why common opinion holds that God is an animal which is eternal and best; for around us life is clearly apparent only in animals, and therefore God is called an animal because life belongs to Him…”  (In XII Metaphys. L. 8, 2544)


This places in perspective Aristotle’s teaching that the first mover causes motion in the way that the desirable and intelligible are found to cause motion, for only these cause motion without being moved. (Metaphysics Bk. XII, ch. 7, 1072a 26 et seq.)  And St Thomas says something further to the point.

“It should also be noted that Aristotle says here that the necessity of the first motion is not absolute necessity but necessity from the end, and the end is the principle which he later calls God inasmuch as things are assimilated to God through motion.  Now assimilation to a being that wills and understands (as he shows God to be) is in the line of will and understanding, just as things made by art are assimilated to the artist inasmuch as his will is fulfilled in them.  This being so, it follows that the necessity of the first motion is totally subject to the will of God.”  (In XII Metaphys. L. 7, 2535)


In Metaphysics Bk. VI Ch. 1 1025b 3-1026a 32, in the course of insisting on the proper science we now call ‘Metaphysics’, Aristotle says this:

“First philosophy… deals with things which are both separable from matter and immobile.  Now, common causes must be eternal, and especially these; since they are the causes of the sensible things visible to us”.

St Thomas’s comment on the text is apposite—

“Now common causes must be eternal, because the first causes of beings which are generated must not themselves be generated, otherwise the process of generation would proceed to infinity; and this is especially true of those causes which are altogether immobile and immaterial.  For those immaterial and immobile causes are the causes of the sensible things evident to us, because they are beings in the highest degree, and therefore are the causes of other things as [Aristotle shows in Book II]…  [F]rom this it is quite evident that the opinion of those who claimed that Aristotle thought that God is not the cause of the substance of the heavens, but only of their motion, is false.”  (In VI Metaphysics L.1, 1164)

His Grasp of the Real Distinction

That Aristotle understood the distinction between essence (what something is) and existence (that something is) is clear from what he has to say in Metaphysics Book II Ch. 1, 993b 19, et seq. where he deals with the knowledge of ultimate causes.

“[T]he principles of things that always exist must be true in the highest degree because they are not sometimes true and sometimes not true.  Nor is there any cause of their being, but they are the cause of the being of other things…”


This is confirmed in St Thomas’s commentary:

“[T]he principles of things which always exist, i.e., the celestial bodies, must be most true… First, they… surpass the truth of things subject to generation and corruption, which sometimes exist and sometimes do not.  Second, these principles have no cause but are the cause of the being of other things.  And for this reason they surpass the celestial bodies in truth and in being; and even though the latter are incorruptible, they have a cause not only of their motion, as some men thought, but also of their being, as the Philosopher clearly states…”  (In II Metaphys. L. 2, 295)


His grasp of the distinction is clear elsewhere.  Nothing illustrates it better than living things, for essence and existence come and go in them with regularity.   In the De Anima, Bk. 2 Ch. 4, Aristotle says this:

“The soul is the cause and the principle of the living body.  Now these words can be used in many ways.  The soul, however, is the cause in three established senses: for it is that whence comes movement; that ‘for the sake of which’; and as the essence of living bodies.  (415b 8-12)

“That it is as the essence is evident.  For in all things the essence is the cause of existence.  In things that live, to live is [the same as] to be; and the cause and principle of this is the soul.”  (415b 12-14)

St Thomas comments:

“[T]he cause of anything as its ‘essence’, i.e., form, is the same as the cause of its being, for everything has actual existence through its form.  Now it is the soul that gives being to living things, for their being is precisely their life which they have from the soul.  Hence the soul causes the body as its form.”  (In II De Anima L. VII, 319-320)


At its conception essence and existence coalesce in the living being.  Its instrumental efficient cause is the parents through whose action it is produced.  But its principal efficient cause is God for “intermediate things in a series limited by some first and last thing must have as their cause the first member of the series…  if there is nothing first in the whole series nothing in the series is a cause.”  (994a 11 to 994b 31)  Thus it is God who gives the new living being essence and existence through the parents’ instrumentality.  And, since the living being is not its own act of existence, it is held in being by God while ever it lives.



[1]  Phoenix from the Ashes, Kettering, Ohio (Angelico Press), 2015, p. 25.

[2]   Dr A M Woodbury SM, Ph.D, STD, who founded Sydney’s Aquinas Academy, commented on this passage that Aristotle distinguished rigorously between a created intellect capable of understanding, “an understand-er”, and God Who is ever actually understanding.